1. Field of the Invention
This invention relates to a mechanical mounting for a zoom lens and, more particularly, to a mechanism for moving, for example, a variator and a compensator when zooming.
2. Description of the Related Art
The conventional mechanical mounting for zoom lens is constructed as shown in FIG. 7. In the case of the type having a focusing lens L.sub.1, a magnification varying lens L.sub.2, a compensation lens L.sub.3, and an image forming lens L.sub.4, the focusing lens L.sub.1 is carried on a focusing lens holder 1. This focusing lens holder 1 is linked to a lens fixing barrel 2 by a helicoid connection so that the focusing lens L.sub.1 is axially moved by rotating the focusing lens holder 1.
Also, the magnification varying lens L.sub.2 and the compensation lens L.sub.3 are held in lens holders 3 and 4, respectively. These lens holders 3 and 4 have peripheral penetration holes freely slidable on guide bars 5a and 5b so that they can axially move. The movable amounts of the magnification varying lens L.sub.2 and the compensation lens L.sub.3 are controlled by camming slots 6a and 6b bored in a cam sleeve 6 rotatably fitted in the inner diameter of the lens fixing barrel 2. The cam sleeve 6 is linked to rotate in response to the rotation of a zoom operating ring 7 fitted on the outer periphery of the lens fixing barrel 2 through a convex portion 7a provided in the zoom operating ring 7. Shaft rollers 3a and 4a which are fixedly mounted on the lens holders 3 and 4 engage in the camming slots 6a and 6b of the cam sleeve 6, respectively. By rotating the zoom operating ring 7, the lens holders 3 and 4 are linearly moved along an optical axis in response to the respective loci of the camming slots 6a and 6b.
Incidentally, in such a zooming mechanism, the cam sleeve 6 uses metal material such as aluminum, and the camming slots 6a and 6b of uniform width are formed in the cylindrical surface by machining.
For this reason, the production cost of the cam sleeve 6 becomes high. Also, because the cam sleeve 6 is made up of metal, the total weight of the lens mounting tends to become heavy. Thus, the cam sleeve 6 has been an obstacle to a reduction of the cost and weight of the lens mounting.
So, recently a proposal has been made that this cam sleeve is formed in a mold by using synthetic resin (plastic) material to achieve the reduction of the cost and weight. But, since the camming slots which can be said to be the heart of the zoom lens control, necessitate very high precision fabrication, the production technique of this kind hardly enables the required cam lift accuracy and camming slot uniformity to be obtained. Another drawback was that, because the use of the slots make the structure of the mold complicated, the price of the mold became high.
Also, as an improved proposal, U.S. Pat. No. 4,386,829 is known. This proposal is that the cam of the cam sleeve is formed to a ridge and, further, pressing means in the form of a spring is provided for enabling the cam follower to slide always on one shoulder of the cam ridge, thereby giving an advantage that the cost of the cam sleeve is lowered, the accuracy of camming movement is improved, and the attitude difference is limited to a minimum.
It should be noted, the same improvements may otherwise be achieved as in U.S. Pat. No. 3,506,338 and Japanese Utility Model Publication No. Sho 60-41533.